#include<bits/stdc++.h>
#define REP(i,n) for(int i=0,i##_len=(n);i<i##_len;++i)
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
#define All(x) (x).begin(),(x).end()
using namespace std;

int main(){
    int N,K;cin>>N>>K;
    K--;
    vector<long long> X(N),A(N);
    REP(i,N) cin>>X[i];
    REP(i,N) cin>>A[i];
    vector<long long> ranl(N),ranr(N);
    REP(i,N) {
        ranl[i]=X[i]-A[i],ranr[i]=X[i]+A[i];
    }
    int l=K-1,r=K+1;
    long long left=ranl[K];
    long long right=ranr[K];
    while(0<=l||r<N){
        bool nuke=true;
        if(0<=l&&left<=X[l]){
            nuke=false;
            left=min(left,ranl[l]);
            right=max(right,ranr[l]);
            l--;
        }
        if(r<N&&X[r]<=right){
            nuke=false;
            right=max(ranr[r],right);
            left=min(left,ranl[r]);
            r++;
        }
        if(nuke) break;
    }
    cout<<r-l-1<<endl;
}